This application claims the priority of German application No.10012976.5-43, filed Mar. 16, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for the adhesive bonding of a sensor assembly backing plate to a vehicle window, especially to a windscreen of a vehicle, for example a passenger car, a truck, an aircraft or a ship.
Preferred embodiments of the invention relate to a method for the adhesive bonding of a backing plate for a sensor assembly to a vehicle window, especially a windscreen of a passenger car or truck, the backing plate having an adhesive layer and being heated at least in the area of the adhesive layer by a heating device until the adhesive layer is sufficiently softened for the formation of an adhesive bonded connection, the backing plate being transferred into a contact pressure device, the contact pressure device pressing the backing plate with the adhesive layer on to the vehicle window for a predetermined length of time.
In modern passenger cars a sensor assembly containing a light sensor, a rain sensor or distance measuring device, for example, may be fitted to the windscreen. To do this, the sensor assembly or constituent parts thereof are mounted on at least one backing plate, which is in turned fixed to the windscreen by adhesive bonding. For this purpose the backing plate is furnished on one side with an adhesive layer, which must first be heated in order to form an adhesive bonded connection. Such an adhesive layer may consist, for example, of a double-sided, transparent silicone adhesive pad. In order to prevent contamination of the adhesive layer, this is provided with a protective film, which must be removed before adhesive bonding of the backing plate to the windscreen. This protective film generally takes the form of a so-called xe2x80x9clinerxe2x80x9d. At present adhesive bonding of the backing plate is performed as follows:
A number of backing plates are provided in a storage container. The backing plates are individually and manually taken from the storage container and placed in an oven. In the oven a number of carrier plates and hence their respective adhesive layer are heated until the adhesive layer is sufficiently softened for adhesive bonding. This heating process has hitherto taken approximately 50 minutes in such an oven. The backing plate is then taken manually out of the oven, following which the protective film must be manually removed before the backing plate is inserted or transferred into a contact pressure device. Finally this contact pressure device presses the backing plate on to the vehicle window for a predetermined length of time. This method currently employed requires a relatively large proportion of manual operations, which call for great care, for example when stripping off the protective film. The entire process from taking the backing plate out of the storage container to completion of the contact pressure sequence to form the adhesive bonded connection currently takes approximately 1 hour. This known method is consequently labor-intensive and unsuitable for series production as part of a mass production process.
The present invention addresses the problem of designing a method of the aforementioned type in such a way that it can be used in the context of mass production.
According to the invention this problem is solved by a method of the above referred to type, wherein the heating device has a heater operable to emit infrared radiation, heating of the layer of adhesive being carried out until it has softened sufficiently by positioning the backing plate with the adhesive layer facing the heater relatively close to the heater for a predetermined length of time.
By using means for the emission of infrared radiation it is possible, in a relatively short time, to heat the adhesive layer so that sufficient softening occurs to carry out the adhesive bonding. In order to achieve such brief, intensive heating, the backing plate is positioned in front of the infrared emitter/radiator so that the adhesive layer is facing the infrared emitter/radiator and situated at a relatively short distance therefrom. The transmission of heat energy by means of infrared radiation over a relatively short distance is referred to as xe2x80x9cNear Infrared technologyxe2x80x9d or xe2x80x9cNIR technologyxe2x80x9d. The time taken for sufficient softening of the adhesive layer can consequently be reduced to approximately 20 seconds. The method according to the invention can accordingly be carried out with sufficient speed to be used in the context of mass production.
According to an advantageous embodiment the backing plates can be preheated by means of a preheating device before transferring them to the heating device. The said preheating of the backing plates is preferably carried out at a time when the backing plates are still in their storage container. The NIR technology used to heat the backing plates to a predetermined temperature, possibly through a transparent wall of the storage container or a wall transmitting NIR radiation, is also suitable for this preheating. The preheating temperature may be 40xc2x0 C., for example.
In an advantageous development a protective film, which is applied to the adhesive layer of the backing plate, is removed by the heating device prior to heating of the layer of adhesive. In this way damaging and contamination of the softened layer of adhesive due to stripping-off or removal of the protective film can be prevented. When removing the protective film, the risk of damage or contamination of the adhesive layer is significantly reduced if the adhesive layer has not yet been heated.
According to an especially advantageous embodiment the protective film is affixed to the storage container in such a way that the protective film is automatically stripped off the adhesive layer as the backing plate is taken out. This measure obviates the need for careful handling in order to remove the protective film, so that this process can be performed with less care and hence carried out mechanically, for example by a robotic arm. According to a development the protective film can be adhesively bonded to the storage container, for example, in order to produce the above-mentioned affixing. In another embodiment the protective film can be adhesively bonded to a film substrate, the film substrate in turn being detachably fixed to the storage container. This detachable fixing can be achieved in particular by clipping the film substrate to the storage container. This measure greatly facilitates reuse of the storage containers.
According to a particularly advantageous embodiment, the adhesive layer can be heated until it is sufficiently softened by routing the traverse path for transferring the backing plate into the contact pressure device along the aforementioned means for the emission of infrared radiation. In this way the adhesive layer is exposed to the infrared radiation for the predetermined length of time, so that the requisite heat energy transfer coincides with transfer of the backing plate into the contact pressure device. This measure affords improved process control.
The length of time required from taking the backing plate out of the storage container to completion of the contact pressure sequence for pressing the backing plate on to the vehicle window can be reduced to approximately 1 minute, particularly with the provision of preheating.
Further important features and advantages of the method according to the invention will follow from the subordinate claims, from the drawings and from the associated description of the figures referring to the drawing.
It goes without saying that the aforementioned features and those still to be explained below may be used not only in each of the combinations specified but also in other combinations or in isolation without departing from the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.